Alkaline detergent



Patents Dec. 1, 1942 I l E DETERGENT Charles Schwartz, Pittsburgh, Pa., assignor to Hall Laboratories, Inc., Pittsburgh, Pa., a cor poration of Pennsylvania No Drawing. Application May 1, 1939,

- Serial No. 271,179

9 Claims.

kalies. corrode and dissolve the metals quite readily.

Many efforts have been made to utilize the excellent detergent properties of highly alkaline mixtures and at the same time to prevent, in so far as possible, the attack upon soft metals. Thus the use of certain silicates has been successful in decreasing to a considerable extent the corrosion of aluminum in alkaline solutions. It is necessary, however, to be very careful in the choice of silicate used and in the concentration of the solution in order to avoid very serious attack upon the-metal being washed. If the conoentrating of the solution is too high or too low, it attacks the aluminum and this places a serious limitation on the type of solution which may be employed.

Silicates have been used 'also for cleaning tin but in this case the alkalinity of the cleaning solution must be adjusted to so low a pI-I and the temperature of cleaner dropped to such an exsuggested also. In the case of tin, the use of sodium sulphite has become quite widespread in recent years. This material decreases the oxygen concentration of the cleaning solution and inhibits the corrosion of tin by akalies. However, there is considerable corrosion after the sulphite is depleted, as it is very shortly in usual practice. Where the solution is heated in contact with air, the sodium sulphite is readily converted into sodium sulphate, which is ineilective in preventing corrosion.

Probably the most successful remedy for corrosion which has been found thus far has been the addition of chromates or ,dichromates to alkaline materials in the washing of'soft metals. While in general these materials are quite successful in preventing corrosion, they have two serious drawbacks. They tend" tocoat the metal being washed a greenish yellow film which in most cases is very undesirable. Most people are sensitive to chromates and the operators {"3 using the cleaners frequently suffer from what is known as chromic ulcers, which necessitate cessation of all work with material containing chromates and which require long periods of time for healing.

It is an object of the present invention to provide means by which alkaline detergents may m made safe for cleaning soft metals. The present invention has many advantages over the methods previously employed. Aluminum, tin, zinc, lead, cadmium or other soft metals or alloys thereof may be treatedwith solutions'of extremely high pH at boiling temperatures for long periods of time without showing any evidence of corrosion. The cleaning solutions preferably have a pH of at least 10 and in many cases the pH is as high as 12 or over. The corrosion inhibitors which I employ do not decrease in effectiveness with time, as do the sulphites, but remain eflective over long periods. They are without harmful effect upon the human skin and will not occasion the difficulties accompanying the use of chromates or dichromates.

I have found that the watersoluble salts of lead when added in proper proportion to alkalies containing an alkali-metal silicate as its principal alkaline ingredient prevent entirely the characteristic corroding efiect of these silicates. The mechanism whereby the corrosion is prevented is unknown but it probably can be ascribed to the formation of non-reactive protective films on the metal surfaces.

Sodium metasilicate, sesquisilicate and orthosilicate are strong alkalies, their alkalinity increasing in the order listed. It is well known that even the weakest of these, namely, sodium metasilicate when used for example to wash tin or tin platecauses rapid spangling and solution of the tin even at relatively low temperature. I have found that by adding a small quantity of a water-soluble lead salt to any of these silicates the corrosive effect of the solution subsequently made from it is reduced to zero even at boiling temperatures over long periods of time.

While lead nitrate is the preferred water-soluble salt for inhibiting the corrosion of the metal, I may employ any lead salt which is ordinarily soluble in water. Among the water-soluble lead salts which may be used are the acetate and the basic lead acetate. The amount of lead salt best suited for the purpose will depend upon the metal to be treated, the treating solution and the conditions of treatment. Ordinarily the lead salt should be used in an amount equal to at least l0% -based on the. weight of the alkali-metal silicate. Preferably it will be 15% or 20% or more where the metal is to be boiled in the silicate solution- When the cleaning solution is used at low temperatures it is possible to decrease the amount of lead salt even below the lowest figure previously given.

The silicate solution containing the corrosion inhibitor is useful in all cases where a highly alkaline detergent is required. It may be used for example in the washing of tin plates, tubes, bakery pans, milk cans, and in tin fabricating plants. In the fabrication of tin plate, or articles made therefrom, it is often necessary to apply grease to aid in the forming operations. This may be removed by the use of a highly alkaline cleaning solution in accordance with the present invention without attack on the tin. The cleaning solutions may be used also in the treatment of aluminum. In this case, also, the solution may be used to remove the grease employed in fabricating the aluminum without, however, causing alkaline corrosion of the aluminum.

For washing pans in a bakery where the pans are washed fairly frequently, so that the amount of burned on matter is not excessive, I may use a cleaning composition containing about 95% sodium metasilicate and lead nitrate or other water-soluble lead salt. This is dissolved in water to form a solution of a strength between' of 1% and 3%. Sodium metasiiicate, sesquisilicate or orthosillcate are generally employed in 1% solutions. In cleaning the bakery pans, they might be boiled in the cleaning solution for an hour.

Where the deposits on the bakery pans are excessive, I might use an aqueous solution of a composition containing 95% sodium orthosilicate and 5% lead nitrate or other water-soluble lead salt and boil the pans for an hour in that solution. The solution containing the sodium orthosilicate is more alkaline than that containing the metasilicate.

As another example, I might use a 1% aqueous solution of a composition containing 60% sodium metasilicate, 35% sodium hydroxide and 5% of lead nitrate or other water-soluble lead salt where a highly alkaline solution is desired. I might add to this or to any of the compositions, a wetting agent such as a sodium salt of a sulplated fatty alcohol in the amount of 1-3%,

based on the total weight of the solids.

The lead salts also act as inhibitors in the presence of mixtures of silicates with sodium hydroxide or other alkalies, soap, casein, defiocculating agents, wetting agents, abrasives and the like.

I have found that the presence of silicate is necessary for the action of the lead in inhibiting corrosion but that it is possibl to add other alkalies to the silicates. A 1% solution of trisodium orthophosphate corrodes tin at boiling temperature in three minutes Even if lead nitrate is added to such solution, it does not prevent corrosion of .the tin, irrespective of the amount added.

Similar tests using alkalbmetal carbonates as the alkaline solution have shown that the inhibitors are ineffective in preventing corrosion of the metal in the absence of silicates. The inhibitors to be effective must be used in a composition containing at least 50% of an alkali-metal silicate, although the amount of silicate required must be determined in each case and depends upon the nature of the materials added to it and the conditions under which the mixture is to be used.

I have found that in all cases it is necessary that the alkaline solution contain an alkali-metal silicate as its principal alkaline ingredient, in

order for the inhibiting agent to be effective.

metal to be treated andthe conditions of treatment. Under severe conditions, the amount of other alkali which is used must be comparatively small, whereas under less severe conditions it may be increased. For example, if the detergent contains sodium metasilicatev and trisodium orthophosphate and is to be used in cleaning tin by heating the tin for one hour at boiling temperature, the metasilicate being used in a 1% solution, I could use about 5% of the trisodium orthophosphate based on the weight of the metasilicate. Theproportion of trisodium phosphate could be increased under less severe conditions or if a less alkaline material than trisodium orthophosphate was employed, I might use a larger proportion of it.

The invention enables the use of highly alkaline solutions containing alkali-metal silicates in the cleaning of soft metals without corrosion of the metal. Although the invention has been described particularly in connection with preventing the corrosion of aluminum and tin, it is applicable also to the treatment of zinc, lead; cadmium or other soft metals or alloys thereof. The term soft metal" as used herein is intended to include any metal or alloy which under the proper conditions of temperature and concentration tends to be attacked or dissolved by alkaline solutions.

The invention is not limited to the examples, which have been given merely for illustrative purposes, or to the preferred proportions, but maybe otherwise embodied or practiced within the scope of the following claims.

I claim:

1. An alkaline detergent composition for soft metal, comprising by weight about 95% sodium metasilicate and about 5% of a water-soluble lead salt.

2. An alkaline detergent composition for soft metal, comprising by weight about 95% sodium metasilicate and about 5% lead nitrate.

3. An alkaline detergent composition for soft metal, comprising by weight about sodium orthosilicate and about 5% of a water-soluble lead salt.

4. An alkaline detergent composition for soft metal, comprising by weight about 95% sodium orthosilicate and about 5% lead nitrate.

5. An alkaline detergent composition for soft metal, comprising by weight about 60% sodium metasilicate, about 35% sodium hydroxide and about 5% lead nitrate.

6. An alkaline detergent composition for soft metal, comprising by weight about 60 to 95% sodium metasilicate, an effective amount up to about 35% sodium hydroxide and about 5 to 20% of a water-soluble lead salt.

7. An alkaline detergent composition for soft metal, comprising by weight about 60 to 95% alkali-metal metasilicate, an effective amount up to about 35% alkali-metal hydroxide and about 5 to 20% of a water soluble lead salt.

8. An alkaline detergent composition for soft metal, comprising by weight at least 50% up to 95% alkali-metal metasilicate, an effective amount up to about 35% alkali-metal hydroxide and about 5 to 20% of a water soluble lead salt. 1

of the soft metal.

. CHARLES SCHWARTZ. 

